Permanent magnet-type synchronous motors are used for general purposes (see, for example, Patent Literature 1 and Patent Literature 2).
With a method of controlling a permanent magnet-type synchronous motor, which is described in Patent Literature 1, a temperature detector is embedded in a winding of the permanent magnet-type synchronous motor to indirectly detect a temperature Tmg of a magnet so as to obtain an interlinkage magnetic flux number φm of the winding by using an interlinkage magnet table with respect to the temperature. An Id calculation unit calculates, from the winding interlinkage magnetic flux number φm, a q-axis current command Iq*, and a rotation speed ω, and other values, a d-axis current command Id* that allows a voltage to be kept constant even when φm changes.
With a vector control method for an AC motor, which is described in Patent Literature 2, when an absolute value of a d-axis voltage command value Vd* becomes larger than a limit value Vdlim thereof, a voltage command value limitation unit limits the d-axis voltage command value Vd*. When a length Vl* of a synthetic vector of the d-axis voltage command value Vd* and a q-axis voltage command value Vq* still exceeds a limit value thereof, the voltage command limitation unit corrects the length Vl* of the synthetic vector to a preset limit value or smaller.